In most paper handling equipment (such as: printers, copiers, facsimile machines, mailing machines, inserters, etc.) there is an apparatus for repeatedly feeding sheets from a supply or stack of sheets. Paper handling equipment is typically characterized by the functions it performs and the different types of sheets (cut copy or print sheets, original sheets, envelopes, post cards, checks, etc.) which it operates on. Generally, it is desirable to remove a single sheet from the stack and thereafter perform one or more functions on the sheet. The process of removing an individual sheet from the stack is commonly referred to in the industry as singulation or separation and the apparatus which performs this function is commonly referred to as a sheet feeder, singulator or separator. As the singulation process is repeated, a stream of individuals sheets is created. In this manner, a high degree of automation is achievable.
The efficiency of the sheet feeder is measured by: (1) its ability to consistently singulate and feed sheets from a stack without producing misfeeds; and (2) the speed at which the sheet feeder operates. One type of common misfeed to be avoided is a multi-feed which occurs when two or more sheets are removed from the stack and fed downstream together. This causes problems for the paper handling equipment, such as jams, which often require operator intervention to correct. Another type of common misfeed is a stall which occurs when the sheet feeder fails to feed any sheet at all. Therefore, it is desirable to have the sheet feeder operate within a processing window between stalls and multi-feeds where only single sheets are fed downstream.
Additionally, it is desirable to have the sheet feeder operate at high speed so that overall throughput of the paper handling equipment is achieved. Thus, a reliable and fast sheet feeder results in more efficient and cost effective paper handling equipment. However, increasing the speed of the sheet feeder often has the resulting negative consequence of increasing the likelihood of misfeeds. Additionally, the problem of misfeeds is complicated by a number of other factors. For example, static electricity, adhesion/cohesion and frictional drag between the sheets all act to generate a tendency for the sheets to remain together and resist singulation.
In addition to the factors above space is usually at a premium, thus it is desirable to achieve the maximum capacity of a sheet feeder given a fixed space. Multiple existing sheet feeders employ an elevator or other lift mechanism to increase the capacity of the feeder. Such mechanisms support the stack of sheets and advance the sheets to the feeder based on a demand signal from the feed system. It is also advantageous to design the lift mechanism so the lift mechanism can be de-coupled from the paper tray which enhances the service and manufacture of the feed system. It is also desirable to provide adequate user access for reloading the feed system with sheets. Existing feeders typically utilize a linear lift mechanism which require that the components and structure encompass the paper tray, which limits access and can prohibit the decoupling of the tray assembly from the lift mechanism.